Aligned liquid crystals are widely used in flat panel display technology. They are aligned by inducing anisotropy on the surface of a substrate. This surface is usually a polymer layer such as polyimide, coated on a glass substrate, as discussed in D.-S. Seo, H. Matsuda, J. Ishizaki, Y. Lamura and S. Kobayashi, SID Digest 1993, p. 953. Conventionally, there are a number of ways of introducing anisotropy on the surface. They include rubbing (see O. Kehmann (1906) and P. Chatelain (1943), cited by P. G. deGennes and J. Prost, "The Physics of Liquid Crystals," Clarendon Press, Oxford (1993) p. 109, 161), stretching a polymer (as discussed in H. Aoyama, Y. Yamazaki, M. Matsuura, H. Mada and S. Kobayashi, Mol. Cryst. Liq. Cryst. 72, 127 (1981)), a Langmuir-Boldgett film (see H. Ikeno, A. Oshaki, M. Nitto, N. Ozaki, Y. Yokoyama, K. Kakaya and S. Kobayashi, Jpn. J. Appl. Phys., 27, L475, (1988)), a grating structure produced by microlithography (see M. Nakamura and M. Ura, J. Appl. Phys., 52, 210 (1981)), oblique angle deposition of SiOx (see J. lenuing, Appl. Phys. Lett., 21, 173 (1982)) and polarized UV radiation of polymer films (see M. Schadt, K. Suhmitt, V. Kozinkov and V. Chiqvinov, Jpn. J. Appl. Phys., 31, 2155 (1992)).
Most of these methods are impractical due to their complexity and/or cost for mass production. The pervasive method used in aligning liquid crystal displays available on the market today is the mechanical rubbing treatment (with, for example, a velvet cloth) of a polyimide film which is coated on the substrate. As discussed in S. Kobayashi and Y. limura, SPIE, 2175, 123 (1994), this method has several drawbacks. First, debris is left by the cloth during the rubbing process, damaging an otherwise clean room environment. Second, the vigorous rubbing may damage (e.g. scratch) the structure of the cell. Third, electrostatic discharging may influence the electronic circuitry below the thin polyimide film. Fourth, stability and consistency of pretilt angle are difficult to achieve and control. Finally, rubbing, being a macroscopic process, does not readily lend itself to aligning liquid crystals in different directions at the spatial size of a pixel, which is usually of the order of a hundred micrometers. This local alignment is desirable to obtain a multidomain structure, which significantly increases the angle of viewing of the display. The limited angle of viewing of current liquid crystal displays is one of the limitations of this technology.
It is an object of the present invention to provide a liquid crystal display cell produced by an improved method of providing a characteristic to a surface to which liquid crystal molecules align.
It is another object of the present invention to provide a liquid crystal display cell with such characteristic provided by using a particle beam, such as an atomic or ion beam.